Paper‐Based Laser‐Pyrolyzed Electrofluidics: An Electrochemical Platform for Capillary‐Driven Diagnostic Bioassays

Abstract

Microfluidic paper-based analytical devices (μPADs) are indispensable tools for disease diagnostics. The integration of electronic components into μPADs enables new device functionalities and facilitates the development of complex quantitative assays. Unfortunately, current electrode fabrication methods often hinder capillary flow, considerably restricting μPAD design architectures. Here, laser-induced graphenization is presented as an approach to fabricate porous electrodes embedded into cellulose paper. The resulting electrodes not only have high conductivity and electrochemical activity, but also retain wetting properties for capillary transport. Paper-based electrofluidics, including a lateral flow device for injection analysis of alkaline phosphatase in serum and a vertical flow device for quantitative detection of HPV16 with a CRISPR-based assay are demonstrated. It is expected that this platform will streamline the development of diagnostic devices that combine the operational simplicity of colorimetric lateral flow tests with the added benefits and possibilities offered by electronic signaling.

Tuning the Chemical and Electrochemical Properties of Paper-Based Carbon Electrodes by Pyrolysis of Polydopamine

“…As-deposited PDA converts the hydrophobic surface of the PP electrode into superhydrophilic, allowing capillary flow of aqueous solutions through the porous material. This new method delivers capillary-through using biocompatible PDA without the need of prior dropping of alcohols 44 or hydrophilic layers 45 underneath the carbon electrode. In addition, since conductivity is important to further improve the performance of electrochemical sensors, 79 the pyrolysis process can promote a graphitization of PDA and tune the chemical composition of the interface.…”

“…This feature is particularly important to allow capillary-driven aqueous solutions in hydrophobic and porous pyrolyzed carbon electrodes. By controlling the flow-through in these electrodes it is possible to tune the area of electrodes, , filtrate samples, and fabricate three-dimensional (3D) devices by stacking multiple sheets of paper . These features were recently studied by dropping isopropanol or surfactants before the analysis and by using O 2 plasma to allow capillary-driven of aqueous solutions .…”

Rapid Electrochemical Flow Analysis of Urinary Creatinine on Paper: Unleashing the Potential of Two-Electrode Detection

“…In the realm of point-of-need testing, paper-based FIA devices have attracted considerable attention due to low fabrication costs and their passive, pump-free operation. , Because of the difficulty of fabricating electrodes in cellulose paper, early attempts to incorporate electrochemical sensing into paper-based FIA relied on the use of external electrodes in contact with the fluidic path. − Such a strategy essentially undermines the advantage of paper as a single-use substrate since the external electrodes are reused multiple times, raising the risk of cross-contamination. To address this shortcoming, we recently developed laser-pyrolysis of cellulose as a versatile technology for fabricating electrodes fully embedded into paper . Despite their advantages, the electrochemical sensors fabricated in this manner still relied on a three-electrode configuration, with a laser-induced graphenized (LIG) pseudoreference, resulting in signal aberration in continuous flow assays …”

“…To address this shortcoming, we recently developed laser-pyrolysis of cellulose as a versatile technology for fabricating electrodes fully embedded into paper. 16 Despite their advantages, the electrochemical sensors fabricated in this manner still relied on a three-electrode configuration, with a laser-induced graphenized (LIG) pseudoreference, resulting in signal aberration in continuous flow assays. 16 The adoption of two-electrode, or reference-free, electrochemical sensors has the potential to address many of the challenges associated with the use of pseudoreferences in FIA.…”

“…16 Despite their advantages, the electrochemical sensors fabricated in this manner still relied on a three-electrode configuration, with a laser-induced graphenized (LIG) pseudoreference, resulting in signal aberration in continuous flow assays. 16 The adoption of two-electrode, or reference-free, electrochemical sensors has the potential to address many of the challenges associated with the use of pseudoreferences in FIA. Moving to two-electrode systems would substantially simplify device fabrication and readout hardware by eliminating the need for a reference potential altogether.…”